At present, EAP (Electro Active Polymers) based actuators and generators (i.e. EAP based energy converters) are operated by either passive harvesting systems, where the deformation itself of an EAP based deformable body which acts as a variable capacitor, forces a flow of energy, or by active systems that control the electrical field, voltage or charge directly. As the latter approach typically yields higher conversion efficiencies and higher energy densities, it is preferred for especially larger systems or efficiency sensitive (battery-powered) applications.
An active system is for example disclosed in WO 2010/146457.
The way the electric field is established and controlled during the excitation determines the amount of energy that is converted. This is described by energy harvesting cycles (SRI International); at present mainly three distinctive cycles are used in systems that charge and discharge the EAP actively; constant-charge, constant-voltage and constant-field cycles. The focus of these cycles is on the way the power electronic unit (PEU) interacts with the EAP device during stretching or contraction (or relaxation). In these periods, the net electromechanical conversion takes place.
For biasing (charging) and un-biasing (discharging) the EAP based capacitor, the cycles do not describe a specific strategy and charging and discharging are assumed to happen instantly at maximum and minimum stretch, respectively. In many existing systems, not much attention is paid to these conditions. Some systems allow a setting of the current amplitude during charging or discharging, but the (dis)charging time is not optimized for higher energy output given the material loss components nor is the converter power rating which are key for commercialization.
It is therefore an object of the invention to provide a method which overcomes the disadvantages of the prior art.